1995 Volume 44 Issue 4 Pages 218-225
The ACM (Atmospheric Corrosion Monitor) sensors each of which consists of a Fe/Ag-galvanic couple were exposed to marine atmosphere for one year, for the purpose of evaluating the corrosivity of the site. The outputs of the sensors set up at Shimizu in Shizuoka Prefecture, which is regarded as the most moderate of the four exposure sites, were obtained every 10 minutes with temperature and relative humidity, RH. The sensor outputs were analyzed by distinguishing the time for the durations of dew, rain and dry periods in a day. The time durations for dew period and rain period at Shimizu were found to be 3454h and 1705h respectively throughout the year from 1992.7 to 1993.6. Critical humidity for dew, RH*, decreased exclusively from 80% to 50% with the increase of amount of deposited sea salt, Ws. It is thus suggested that the ISO recommendation method is not adequate by which the time of wetness is defined as the time when RH value is at and above 80%. The frequency data of dew period and dry+dew period against RH measured by the ACM sensor will be available to study the rusting for stainless steels. It is considered that corrosivity of each site can be estimated effectively by analyzing the above mentioned factors, especially amount of deposited sea salt, obtained by this ACM sensor.